There is known a rotary damper that generates larger damping torque against rotation in the normal direction and generates smaller damping torque against rotation in the reverse direction. For example, the Patent Literature 1 discloses a rotary damper that is simple in construction and can be produced at low cost.
The rotary damper described in the Patent Literature 1 comprises: a case having a circular cylinder chamber; a rotor rotatably received in the circular cylinder chamber; viscous fluid filled in the circular cylinder chamber; and a lid fixed to the opening-side end surface of the case, to enclose the rotor and the viscous fluid within the circular cylinder chamber.
The rotor comprises: a rotor body of a circular cylinder shape; and vanes, each of which is formed to project outward in radial direction from the outer peripheral surface of the rotor body so as to form a small gap between the vane and the sidewall surface of the circular cylinder chamber. In each vane, is formed a flow path running from vane's one side surface (referred to as first side surface) that is perpendicular to the rotational direction of the rotor to the other side surface (referred to as second side surface). Onto the end surface (i.e. surface facing the sidewall surface of the circular cylinder chamber) of each vane, is attached a seal member to fill the small gap between the vane and the sidewall surface of the circular cylinder chamber. The seal member has a check valve of elastic body, which opens and closes the flow path formed in the vane. On the sidewall surface of the circular cylinder chamber, are formed partition members each projecting inward in radial direction so that a small gap is formed between each partition member and the outer peripheral surface of the rotor body.
In the rotary damper of the above construction described in the Patent Literature 1, when force that rotates the rotor in the direction (normal direction) from the first side surface to the second side surface of each vane is applied to the rotor, the viscous fluid in the circular cylinder chamber presses the check valves respectively against the second side surfaces of the vanes, and the flow paths are blocked by the check valves. As a result, movement of the viscous fluid is limited to only through the gap between the partition member of the circular cylinder chamber and the outer peripheral surface of the rotor body and the gap between the closing-side end surface (i.e. bottom surface) of the case and the lower surfaces (surfaces facing the closing-side end surface of the case) of the vanes. Accordingly, the pressure of the vanes against the viscous fluid on the side of the second side surface becomes a high pressure, and large damping torque is generated. On the other hand, when force that rotates the rotor in the direction (reverse direction) from the second side surface to the first side surface of each vane is applied to the rotor, the viscous fluid flows into each flow path from the side of the first side surface, to push up the check valve concerned and open the flow path. Accordingly, the viscous fluid moves also through the flow paths formed in the vanes, and thus the pressure of the vanes against the viscous fluid on the side of the first side surface does not become a high pressure, and small damping torque is generated.
The rotary damper described in the Patent Literature 1 further comprises a damping force adjustment mechanism for adjusting the larger damping torque generated when force rotating the rotor in the normal direction is applied to the rotor. This damping force adjustment mechanism comprises: an elastic member that is placed between the opening-side end surface of the case and the lid; and a plurality of bolts for fixing the lid onto the opening-side end surface of the case via the elastic member being interposed therebetween. In the opening-side end surface of the case, are formed a plurality of threaded holes. And through-holes are formed in the elastic member and the lid at positions corresponding to the threaded holes. Bolts are inserted into the respective through holes in the lid and the elastic member, and screwed into the respective threaded holes formed in the opening-side end surface of the case. The degree of pushing the rotor by the lid into the inside of the circular cylinder chamber of the case is adjusted by the degree of screwing of the bolts. As a result, the gap between the closing-side end surface of the case and the lower surfaces of the vanes is adjusted, and this makes it possible to adjust the larger damping torque generated when force rotating the rotor in the normal direction is applied to the rotor.